Passively compliant legs have been instrumental in the development of dynamically running legged robots. Having properly tuned leg springs is beneficial for stable, robust and energetically efficient running at high speeds. Recent simulation studies indicate that having variable stiffness legs, as animals do, can significantly improve the speed and stability of these robots in changing environmental conditions.
However, to date, the mechanical complexities of designing usefully robust tunable passive compliance into legs has precluded their implementation on practical running robots. Therefore, there remains a need for improvements in terms of performance in a small, lightweight, and rugged package.